It sounds like the fastest you are used to driving is 80kph. Most of our expressways are 70mph = 112 kph. There are times you will be a traffic hazard if you DO NOT GO FASTER than the speed limit as lines of traffic form behind you. In Detroit, traffic sometime AVERAGES 80 mph (130kph) even though the speed limit is 70. I just drove from Detroit to Brighton and people were riding my tail at 80mph. This is the reality of driving in the USA.
I assume traffic will be similar from NY to Florida. Let's not even talk about construction zones. Save yourself a lot of aggravation and hop a plane.